The invention relates to a device for holding workpieces which is constructed tong-like and is provided with two tong arms, wherein the tong arms are supported by a tong base and can be arranged in a controlled manner in at least one opening position and in a closed position, and wherein the tong base is held by a base element in such a way that the tong base is released once a predetermined adjustment force has been reached, and wherein the tong base is arranged so as to be pivotable at least over sections relative to the base element.
Moreover, the invention relates to a device for blow molding containers which includes at least one blow molding station with a blow mold and at least one support element for positioning preforms along a transport path. In this connection, it may be provided that the support element is held by a rotating transfer wheel relative to which the support element is movably mounted, and wherein a cam control is used for the support element.
When shaping containers by means of the influence of compressed air, preforms of a thermoplastic material, for example, preforms of PET (polyethylene terephthalate) are conveyed within a blow molding machine to different processing stations. Typically, such a blow molding machine includes a heating device as well as a blow molding device in whose areas the previously thermally conditioned preform is expanded into a container by biaxial orientation. The expansion takes place by means of compressed air which is conducted into the preform to be expanded. The process technological sequence of such an expansion of the preform is explained in DE-OS 43 40 291. The introduction of the pressurized gas mentioned in the above introduction also includes the introduction of the compressed gas into the developing container bubble as well as the introduction of the compressed gas into the preform at the beginning of the blow molding procedure.
The basic construction of a blow molding station for forming containers is described in DE-OS 42 12 583. Possibilities for thermally conditioning the preforms are explained in DE-OS 23 52 926.
Within the device for blow molding, the preforms, as well as the blow molded containers, can be transported by means of different handling devices. Particularly useful has been found the use of transport mandrels onto which the preforms are positioned. However, the preforms can also be handled by means of other support devices. The use of gripping tongs for handling preforms and the use of expanding mandrels, which can be inserted into an opening area of the preform, are also among the available constructions.
A manipulation of containers with the use of transfer wheels is described, for example, in DE-OS 199 06 438 in an arrangement of the transfer wheel, between a blow wheel and a discharge section.
The already explained manipulation of the preforms takes place, on the one hand, in the so-called two-stage methods, in which the preforms are initially manufactured in an injection molding process, are subsequently subjected to intermediate storage, and are only then later conditioned with respect to their temperature and blown up into a container. On the other hand, the so-called single-stage method is used, in which the preforms are immediately after their manufacture using injection molding technology and a sufficient solidification, thermally conditioned by suitable means and are subsequently blown up.
With respect to the blow molding stations used, different embodiments are known. In blow molding stations which are arranged on rotating transport wheels, a capability of opening of the mold carriers like a book is frequently found. However, it is also possible to use mold carriers which are slidable relative to each other or are guided in some other manner. In stationary blow molding stations, which are particularly suitable for receiving several cavities for the shaping of containers, typically plates arranged parallel to each other are used as mold carriers.
For the manipulation of the preforms and the manipulation of the blow molded containers, frequently so-called transfer wheels are used within the blow molding machine, wherein the transfer wheels are equipped, with support elements for the preforms or bottles. In this case, the support elements can either grasp the preforms or bottles directly, or convey separate transport elements which, in turn, hold the preforms or the bottles directly. For reinforcing the transfer procedures, the support elements are typically mounted so as to be pivotable relative to the transfer wheel. In addition, a telescoping capability is frequently also realized. Cam controls are used for presetting the position of the support elements. For this purpose, the support elements are guided with cam rollers along stationary cams.
A problem when using such transfer wheels provided with support elements resides in preventing heavy damage due to mechanical problems, particularly when collisions occur. For this purpose, it is known to mount the support arms with the use of overload couplings in the area of the transfer wheels. Such overload couplings are expensive, on the one hand, and, in addition, increase the structural weight of the rotating transfer wheels.
It is also already known to equip the support arms with active positioning elements which pneumatically or electrically preset an extension or retraction of the support arms such that the support arms are arranged in a work position or a position of rest. However, appropriate positioning devices result in relatively high costs and increase the structural weight of the transfer wheel, so that increased inertia properties occur.
Another problem in the use of tong-like support elements resides in the fact that the elements are relatively expensive and, when wear or mechanical damage makes it necessary to exchange the tongs, this requires correspondingly large work expenditure and attendant work costs.
While a tong-like support element is already described in DE 10 2007 054 388, which, under the influence of an overload, is held in the area of a support member so as to be deflectable, however, the respective construction has been found, taking into consideration the large number of required structural elements, to be expensive and, therefore, to only a limited extent, suitable for use in large quantities.